A man rows from A to B (upstream) and B to A ( downstream) in 12 hours. The distance between A and B is 240 km. The time taken by the man to row 6 km downstream is identical to the time taken by him to row 4 km upstream. What is the speed of the stream?

$\frac{35}{3}$ km/h $\frac{25}{3}$ km/h $\frac{46}{3}$ km/h $\frac{50}{3}$ km/h

$\frac{25}{3}$ km/h